[Ron Ramirez]

Most likely, your culprit is bad paper capacitors. It could be a tube...but poor/leaky old caps are more likely to be the problem.

When I do get it working properly, I'm curious if anyone has information on how to change the output stage to provide more volume. I know it would require a bit more work, but I would really like to replace the 50L6 with something with more output.

Why would you want to do that? The 50L6 should provide plenty of volume. You can't expect something like a 38-690, but a 50L6 can easily provide lots of audio, enough that you will only have to turn the volume up a little bit when you have it working properly.

I have a 41-226 "Sled" which has a similar 50A5 (loctal) audio output tube. This radio is actually supposed to have a 35A5, but the 50A5 allows the radio to operate comfortably on today's higher line voltage. Anyway, my 41-226 is plenty loud for me; I never have to turn the volume more than 1/2 of the way up - and most of the time, 1/4 of the way up is plenty loud.